1. Field of the Invention
This invention relates to valves for industrial applications, and more particularly, to a valve having a fire-resistant seal which provides sealing therein when the valve is subjected to heat which can damage other sealing components therein.
2. Description of the Prior Art
Valves for use in controlling the flow of fluid through conduits or pipes are well known. A great variety of valves have been developed for various applications, and many of these are rotary valves which are operated by rotating a valve stem extending from a valve housing. One popular rotary valve configuration is the ball valve which has a rotating ball within a housing. The ball is actuated by a valve stem which is engaged with the ball. When the valve is closed, the ball blocks flow of fluid through the valve, and when the valve is open, a port through the ball is aligned with the inlet and outlet ports of the housing. A major advantage of ball valves is that they have substantially no restrictions therethrough and do not cause any significant pressure drop through the valve which can impede fluid flow.
Standards have been developed for industrial application valves by standards organizations, such as the American Petroleum Institute (API). These standards provide specifications for both design, materials and performance criteria, depending upon the application. It is particularly important in applications handling toxic or flammable fluids that these fluids are not released to the atmosphere in the event of fire or other catastrophe. To this end, a variety of sealing arrangements have been employed. A problem with such previous designs is that they use large radial graphite seals which need continual attention and maintenance to insure that they function when needed. Relatively high constant loading of such seals is necessary to overcome the potential of leakage to the atmosphere. Such high loads necessary to maintain the integrity of the seal result in increasing torque necessary to operate the valve. Further, the graphite seals can cause corrosion on the rotary valve stems, and this further increases the possibility of leakage. Details of some prior art valves will be discussed in more detail herein.
The valve of the present invention eliminates the need for a large graphite seal and the attention that such a seal requires. This is done by replacing the large graphite seal with a more resilient seal material and including a relatively smaller fire-resistant graphite seal which works only in the event of sufficient heat being applied to the valve. The new seal design of the present invention also results in considerably reduced loading and a corresponding reduction in torque necessary to operate the valve.